The present invention relates to devices for viewing images produced by optical gunsights. Specifically, an attachment for an optical gunsight is provided which will permit simultaneous viewing of a gunsight image produced from said gunsight through first and second optical ports.
Devices which attach to a gunsight for viewing an input scene, as well as permitting recording of the scene, are described in the foregoing referenced patent application, as well as in various prior art patents. U.S. Pat. No. 4,732,438 to Orbach et al., assigned to ELBIT Systems, Inc., as well as U.S. Pat. No. 4,993,819 to Moorehouse, describe devices which are directly coupled to the gunsight, and provide multiple ports for viewing the image produced by the gunsight.
The Orbach patent describes a prism structure which will permit split-image optical viewing of the gunsight image. A beamsplitter within the housing is coupled to the gunsight and directs a first image to an observer along the gunsight axis. A second image is produced at right angles to the gunsight axis which is imaged on a solid state image converter. The solid state image converter includes a focusing lens assembly which will permit the second image produced at right angles to the optical gunsight axis to be viewed via a television monitor, or alternatively recorded on video tape.
The foregoing design provides for advantages in maintaining eye relief at a minimum. The device described in U.S. Pat. No. 4,732,438 makes use of a pair of prisms joined together forming a diagonal surface for splitting the image into a direct viewing port, and through an orthogonal port connected to a solid state camera. The use of the prism introduces some artifacts into the viewed image, as well as reduces the field of vision obtainable from the optical gunsight.
The prism includes two prisms joined together along a diagonal surface, forming a semi-reflecting surface for splitting the image from the gunsight. The seams formed between the two prisms diagonal surfaces produce color and other visual artifacts which are seen by an observer using the device. Further, polarization effects occur such that the beamsplitter polarizes the incident image.
There is a reduction in the field of view as the diagonal surfaces only subtend a portion of the gunsight aperture.
Further, a visual dark transmission zone occurs in the center half of the visual field of view due to the reduced light from that portion of the aperture area subtended by common surface area of the two prisms.
In view of the foregoing problems, the present invention has been devised.